> I think the idea of the Frank> Drake crowd is to assume that "they" *want* to talk to "us",

Yea, if "they" want to talk to us at our present level of development,
their signal would be of lower bandwidth.

> Umm... I'm not absolutely sure this is true. Would it not show some> statistical evidence of the multiplexing? I admit it might be subtle, and I

If a light signal were modulated with a significant chunk of the available
bandwidth, say, >1% of it, the modulation would be too fast for our
(standard) detectors to notice. The signal power would be detected,
and the overall power spectum, but not the modulation. If it is modulated
as fast as we are likely to be able to do with nanotech, which I'm
estimating at at least 1 terahertz (based on the reported, computed,
wiggle rates of some nanotech mechanical structures), there is little need
to use the bottom few percent of available bandwidth.

And as I mentioned, the overall power spectrum of the signal could be
disguised as anything else. Some current military spread spectrum
transmissions cannot be distinguished from background noise even if you
plug the output of the transmitter directly into your RF spectrum
analyzer.